Re: [Xen-devel] [PATCH] x86: machine check exception handling

[Keir Fraser <keir@xxxxxxxxxxxxx>]

On 19/6/07 11:06, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> Properly handle MCE (connecting the exisiting, but so far unused vendor
> specific handlers). HVM guests don't own CR4.MCE (and hence can't
> suppress the exception) anymore, preventing silent machine shutdown.
> 
> This patch won't apply or work without the patch removing i386's NMI
> deferral.

Applied with the following changes:
 1. Pulled out the common parts of the NMI/MCE asm handlers into a common
subroutine (like all other execption handlers jump at handle_exception to do
the hard work).
 2. Kept do_machine_check() as analog of do_nmi(), which can hide
machine_check_vector definition (and hence I removed all changes inside
arch/x86/cpu/mcheck). I'd like to keep do_machine_check(), even if it
remains no more than a direct call at machine_check_vector(). We could clean
up machine_check_vector() as a separate patch -- not sure if it's worth it
right now, and maybe we're better off keeping close to original Linux files?
 3. Most contentious, I'm sure: removed VMX changes that would keep
interrupts disabled across NMI/MCE. The reason is simply that SVM does not
bother with this. If there is a requirement that NMI/MCE be called with
particular constraints on EFLAGS, then we should make that clear and fix up
both VMX and SVM in a separate patch. The pain of this is that it would
probably require extra checks on critical vmexit paths. Is it *really* that
bad for #MC to get interrupted?

 -- Keir


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